Popular smoking articles, such as cigarettes, have a substantially cylindrical rod shaped structure and include a charge, roll or column of smokable material such as shredded tobacco (e.g., in cut filler form) surrounded by a paper wrapper thereby forming a so-called “tobacco rod.” Normally, a cigarette has a cylindrical filter element aligned in an end-to-end relationship with the tobacco rod. Typically, a filter element comprises plasticized cellulose acetate tow circumscribed by a paper material known as “plug wrap.” Certain cigarettes incorporate a filter element having multiple segments, and one of those segments can comprise activated charcoal particles. Typically, the filter element is attached to one end of the tobacco rod using a circumscribing wrapping material known as “tipping paper.” It also has become desirable to perforate the tipping material and plug wrap, in order to provide dilution of drawn mainstream smoke with ambient air. A cigarette is employed by a smoker by lighting one end thereof and burning the tobacco rod. The smoker then receives mainstream smoke into his/her mouth by drawing on the opposite end (e.g., the filter end) of the cigarette.
The tobacco used for cigarette manufacture is typically used in blended form. For example, certain popular tobacco blends, commonly referred to as “American blends,” comprise mixtures of flue-cured tobacco, burley tobacco and Oriental tobacco, and in many cases, certain processed tobaccos, such as expanded tobacco, reconstituted tobacco and processed tobacco stems. The precise amount of each type of tobacco within a tobacco blend used for the manufacture of a particular cigarette brand varies from brand to brand. See, for example, Tobacco Encyclopedia, Voges (Ed.) p. 44-45 (1984), Browne, The Design of Cigarettes, 3rd Ed., p. 43 (1990) and Tobacco Production, Chemistry and Technology, Davis et al. (Eds.) p. 346 (1999).
It has been common practice to flue-cure certain tobaccos, such as Virginia tobaccos, in barns using a so-called flue-curing process. Cooper et al., VPI Bull., 37(6), 3-28 (1939); Brown et al., Agric. Eng., 29(3), 109-111 (1948); Johnson et al., Job. Sci., 4, 49-55 (1960); Johnson, Rec. Adv. Tob. Sci., Inag. Vol., 63-78 (1974); Peele et al., Rec. Adv. Job. Sci., 21, 81-123 (1995). Tobacco leaf is harvested, placed in barns, and subjected to the application of heat in order to dry and “cure” the tobacco.
There have been reports of investigations associated with curing conditions within tobacco curing barns. See, for example, U.S. Pat. No. 1,768,142 to Pike et al. Carbon dioxide levels within tobacco curing structures during tobacco curing processes have been monitored. See, Johnson et al., Tob. Sci., 7, 85-92 (1963). Changes in oxygen levels within the atmospheres within tobacco curing structures also have been monitored. See, Watkins et al., Tob. Sci., 6, 92-97 (1962). It has been suggested to introduce oxygen into tobacco curing barns during the flue-curing process. See, U.S. Pat. No. 2,708,441 to Viglione. The effects of chemicals, such ethylene, on tobacco during the flue-curing process also have been studied. See, Sisler et al., Tob. Sci., 17, 68-72 (1973) and Walker et al., Tob. Sci., 29, 92-98 (1985). Nitrous oxides in exhaust gases, particularly from direct fire liquid propane powered heating units, have been implicated with the formation of tobacco specific nitrosamines (TSNA) in flue-cured Virginia tobacco. See, US Pat. App. Pub. 2001/0000386 to Peele and U.S. Pat. No. 6,564,808 to Hempfling et al., which are incorporated herein by reference.
During the growing season, numerous environmental factors, such as the amount of rainfall, can impact the chemical properties of tobacco. For instance, in drought conditions, harvested tobacco leaves exhibit higher nicotine levels and lower levels of carbohydrates; and cured tobacco leaves exhibit higher nicotine levels and lower levels of sugars that serve as precursors to aromatic and flavorful compounds (e.g., pyrazines). In growing seasons where rainfall is above average, harvested tobacco leaves contain greater amounts of carbohydrates, and a more moderate nicotine concentration. As a result, due to the volatile and unpredictable nature of the environmental conditions experienced by the tobacco during the growing season, the chemical properties of harvested tobacco and cured leaf are rarely consistent from one year to the next.
It would be desirable to provide an efficient and effective method for chemically modifying tobacco at an early stage of production, such as during the curing process. It would be particularly desirable to adjust the chemical properties of tobacco in a manner that provides greater consistency despite changes in environmental factors from year-to-year.